PixelForge — Pay-As-You-Go AI Image Generation

AI billing is a correctness problem: a concurrent request must never spend credits twice, and a failed generation must never silently eat money. LumiForge solves both with atomic decrement and automatic refunds, while the dual-path payment flow guarantees credits are issued even if the browser disconnects mid-checkout.

A Bun + Express backend with Zod-validated routes for user, image generation, models, and credits & billing, plus a React 19 frontend with TanStack Query and React Router. Cloudflare R2 stores generated images; Better Auth handles email/password and Google OAuth. Credits, spend, and refunds are tracked per user with a full transaction history.

Prisma models for users, credit wallets, transactions (purchases, spend, refunds), generated images, and trial eligibility. Credit balance is stored and decremented atomically with validation in the same query.

Atomic credit deduction under concurrent requests, mapping real model cost to fair credit pricing, the dual-path payment fulfillment (client verify + webhook fallback) without double-crediting, and server-side trial guardrails to prevent premium-model abuse on the free tier.

Stateless Express API on Render with PostgreSQL; images offloaded to Cloudflare R2 for edge distribution. TanStack Query caches client state. Payment flow is idempotent across both fulfillment paths.

Failed generations trigger automatic refunds. The Razorpay webhook is the fallback path — if the browser never receives the response, credits are still issued and deduplicated.

Transaction history gives a full audit of purchases, spend, and refunds; generation success/failure is tracked per model.

Pay-as-you-go credits over subscriptions for flexibility. OpenRouter over a single vendor for multi-model support. Razorpay webhook + verify over a single path for reliability. R2 over S3 for simpler egress pricing.